The findings, gleaned from four separate studies, are scheduled for publication in the November issue of the journal Psychological Science.

With more than one-third of American workers reporting that their bosses have sabotaged, yelled at, or belittled them, the new study challenges previous assumptions that abusive bosses are solely driven by ambition and the need to hold onto their power.

“By showing when and why power leads to aggression, these findings are highly relevant as abusive supervision is such a pervasive problem in society,” says Nathanael Fast, assistant professor of management and organization at USC and lead author of the study.

During role-playing sessions, study participants who felt their egos were under threat would go so far as to needlessly sabotage an underling’s chances of winning money. In another test, participants who felt inadequate would request that a subordinate who gave a wrong answer to a test be notified by a loud obnoxious horn, even though they had the option of choosing silence or a quiet sound.

Researchers did not rate participants by an objective measure of competency, but by their self-reported level of competency. This allowed them to investigate how feelings of self-worth are tied to workplace behavior.

“Incompetence alone doesn’t lead to aggression,” says Serena Chen, associate professor of psychology at UC Berkeley and coauthor of the study. “It’s the combination of having a high-power role and fearing that one is not up to the task that causes power holders to lash out. And our data suggest it’s ultimately about self-worth.”

Alternately, Chen says, participants who got ego boosts by scoring high in a leadership aptitude test or who recalled an incident or principle that made them feel good about themselves did not react with aggression.

Flattery may not be the best way to soothe a savage boss, the study points out: “It is both interesting and ironic to note that such flattery, although perhaps affirming to the ego, may contribute to the incompetent power holder’s ultimate demise—by causing the power holder to lose touch with reality,” the study concludes.